The present invention relates to spring loaded safety valves, and particularly, to springloaded safety valves of medium or small dimensions in which the closing force is directly increased by the action of a supplemental loading piston upon the valve spring in the valve closing position, due to a pressure control device which releases the pressure shortly before the response pressure is attained.
Spring loaded safety valves are well known which have pneumatic cylinders arranged above the spring housing that operate in conjunction with a piston that is attached to the end of the valve shaft so that each motion of the piston into either a valve opening or closing position is transmitted by way of the valve shaft to a valve shutting part, To control the loading such supplementally loaded safety valve have, according to technical safety rules, at the very least, three separate control means, namely, three impulse transmitters and three control members each equipped with an independent pressure outlet pipe, impulse control and regulating pipe, in order that the supplemental force safely yields when trouble occurs with one of the control means. In one such valve the magnitude of the supplemental loading is dependent upon, and not upwardly limited by, the pressure of the control medium and the supplemental piston surface. Apart from this the valve is structured with the pressure sensing element and a diagram valve acting with the affixed loading cylinder and the three independent control means.
There are also known safety valves with affixed supplementally loading cylinders whose pistons do not directly act upon the valve stem, but rather communicate with the valve stem by way of the valve spring acting upon the valve plug supporting the valve stem. In that case the heaving stroke of the supplemental loading piston is limited by the cylinder so that the supplemental force is no more than 1.2 times the response force, thus, if a disruption occurs in the region in which the supplemental force turns off, the valve plug opens before exceeding the allowed loading. Also in this limited closing force safety valve, according to technical safety rules, there must be at least two separate pressure sensing elements and control valves, so that such safety valves, particularly ones of medium and small dimensions equipped with supplemental loading cylinders, are too bulky. Additionally, in the known safety valves, the magnitude of the supplemental loading cannot be changed on account of the fixed heaving stroke of the piston, as is also true of the manufacturing tolerance, and the adjustment of the valve spring.